1. Field of the Invention
The present invention relates to a multiple source system for use in a measurement system, such as a vector network analyzer (VNA). The source system may consist of one or more stimulus signals and a signal to be used as the VNA receiver's LO. More particularly, the present invention relates to faster relative settling of the sources and cancellation of correlated, or common mode, noise resulting in improved measurement speed and accuracy for the measurement system.
2. Background
Vector network analyzers (VNAs) have been developed by the electronics industry to measure the parameters and characteristics of electronic devices and systems at various frequency ranges including microwave and millimeter wave frequencies. A typical VNA can be used to measure the parameters of various single-port or multi-port microwave devices. The parameters measured by a conventional VNA typically include scattering parameters, insertion loss, and group delay. At least some of these parameters, such as the scattering parameters, can be measured as vector quantities, each of which has a real component and an imaginary component, or alternatively, a magnitude component and a phase component.
Conventional VNAs have been used for measuring the parameters of signals of multi-port devices. In these applications, one or more stimulus signal outputs and a VNA receiver local oscillator (LO) signal are required to measure the response of the device under test (DUT). However, conventional VNAs used with conventional multiple signal sources are not designed with dynamic tracking and do not provide for fast settling of frequencies and phases of intermediate-frequency (IF) signals generated by the receiver.
Furthermore, typical test systems using multiple-signal sources and a conventional VNA without dynamic tracking may contain significant phase noise on the VNA receiver IF signals used to measure the scattering parameters associated with the DUT. The presence of significant IF phase noise results in uncertainties in the measurements. Furthermore, a conventional VNA containing sources and an LO without dynamic tracking will not result in common mode or correlated spurious signals that ratio, or "cancel out" on the IF signals. Furthermore, since use of multiple signal sources without dynamic tracking does not allow the signals to be correlated with each other, their individual settling times, i.e., the duration for the signals to settle to a stable frequency, may vary significantly. Consequently, the relative settling time, i.e., the duration for the difference between the sources to settle to a stable IF frequency, may be long. The long relative settling time results in slower measurement speed.
Therefore, there is a need for a multiple signal source/LO module with dynamic tracking which achieves a fast settling time, eliminates or reduces spurious signals on the IF signals within the source PLL bandwidth, and reduces the IF phase noise within the source PLL bandwidth in order to improve the speed and accuracy of measurements.